Porpoising in Auto/RTL but not other stabilized modes

ArduPlane Plane 4.1
1

Tried Auto and RTL modes today and found heavy but slow porpoising with correspondent automatic throttle compensation. Stabilized, Acro and FBWA modes were all rock steady, ran autotune just to make sure but no change there. Any clues as to this behavior?

Thanks

2

Stabilized, Acro, and FBWA don’t have altitude controllers, only pitch.

TECS tuning?

Airspeed sensor error?

Speed values for the modes are too slow?

Post a log and maybe somebody can see something else.